Production of pulp



Patented May 2, 1933 warren stares PATENT OFFEQE LINN BRADLEY, OF MONTCLAIR, NEW JERSEY, AND EDXVARD 1P. MGKEEFE, O13 PLATTS- BURG, NEW YORK, ASSIGN'OES TO BRADLEY-MCKEEFE CORPORATION, OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK PRODUCTION OF PULP No Drawing. Application filed July 2, 1926, Serial No. 120,241. Renewed January 25, 1930.

This invention relates to the production of wood pulp from wood, and includes improvements in the carrying out of the cooking operation for the production of pulp, as Well as improvements in the treatment of residual liquors for the production of further amounts of cooking liquors therefrom.

More particularly, the invention relates to a combination of processes, in which the residual liquors from one process are utilized for the production of a cooking liquor for the other process or, in part, for the same process, the processes being thus interdependent and of a cyclic character. The processes which are carried out thus in an interdependent and cyclic manner are a sodium monosulfite process and a sulfate process. By reference to a sodium monosulfite process we mean the process of cooking wood with a cooking liquor which contains sodium monosulfite as the principal active ingredient, and without or With the presence of other chemicals in varying amounts, e. g. Nit- S, NaO-H, Na s- Na CO but more particularly the process in which sodium monosuliite is used without any considerable amount of other chemicals. By reference to a sulfate process, We refer to the process in which the active reagents of the cooking liquor consist mainly of caustic soda and sodium sulfid, although the proportions of these chemicals may vary somewhat from those commonly used in the usual so-called sulfate process, and other chemicals in varying amounts may also be present, e. g., sodium sulfite.

In the combined operations of the present invention, the residual liquor from a sodium monosuliite process is treated for the production of a part or all of the cooking liquor for a sulfate process, and the residual liquor from a sulfate process is treated for the production of a part or all of the cooking liquorfor a sodium monosulfite process; and the treatment of the respective residual liquors is so carried out that the other cooking liquor in whole or in part can advantageously be regenerated or produced therefrom.

The residual liquors may be mixed in any suitable proportion prior to concentration and destruction of organic matter; but it is advantageous to concentrate and furnace each residual liquor separately especially where the monosulfite liquor is to have little if any Na s or Na3SgO3 in it; and also where 5 a high Na S is desired in a sulfate cooking liquor.

The cycle of operations may conveniently be considered starting with the sodium monosulfite cooking process, which is described-in our prior applications Serial No. 481,147, filed June 28, 1921; Serial No. 686,137, filed January 14, 1924; and Serial No. 711,857, filed May 8, 1924. In this process, sodium monosulfite is used either alone or with moderate and varying amounts of other chemicals, but the liquor is maintain-ed alkaline to litmus throughout the cooking operation.

The residual liquors from a sodium monosulfite process, are subjected to concentration by evaporation, and the resulting concentrated or dry product is subjected to a calcining or smelting operation under reducing conditions with the result that a product is produced in which the sodium is present, mainly as sodium carbonate and sodium sulfid. The relative amounts of sodium carbonate and sodium sulfid will vary with the conditions of the operation, but a considerable amount of the sulfur originally present in the residual liquor is eliminated and escapes with the gases; and while the sulfur thus eliminated may to a considerable extent "be recovered by scrubbing the stack gases, this eliminated sulfur need not be present in the calcined or smelted product with the result that the sulfur content of the calcined o-r smelted product may be, for example, only about a third or a half that of the sodium monosulfite cooking liquor employed, and may be more or less than this. That is, the amount of sodium present as sodium sulfid in the calcined or smelted product may be greater but is usually considerably less than the amount present as sodium carbonate, although the relative proportions may vary considerably. The sulfur contained in the calcined or smelted product is, however, for the most part, in a form such that it can be directly utilized as an active reagent in a sulfate process, i. e., as sodium sulfid.

The solution obtained from the calcined product or melt by treatment with a regulated amount of water and made up mainly of sodium carbonate and sodium sulfid, either with or Without varying and moderate amounts of other sodium salts, and which may include sodium sulfite, is subjected to a causticizing process with sufficient lime to convert a suitable portion of the sodium carbonate into caustic soda. The result is the production of a solution containing mainly caustic soda and sodium sulfid, which can be utilized in carrying out the cooking step of a sulfate process. If the relative proportions of caustic soda andsodium sulfid thus obtained from the compounds contained in the liquor of the sodium monosulfite process used are not those desired for the cooking step of the sulfate process, or of a modified sulfate process, these proportions can be varied, for example, by adding sodium sulfate before reduction or sodium carbonate to the solution before causticizinggor by adding sodium sulfide or sodium hydroxide thereto. Some sodium sulfite may be added thereto, or produced therein, e. g., by treatment with CaSO The solution of caustic soda and sodium sulfid thus produced or regenerated from the sodium monosulfite residual liquor is utilized in carrying out the cooking operation of a sulfate process. This sulfate process may be carried out in the customary manner and using a cooking liquor of the strength and relative contents and proportions of caustic soda and sodium sulfid, such as is commonly used in the so-called sulfate process. The process may, however, be modified somewhat, along the lines hereinafter pointed out, with certain advantages.

The residual liquor from a sulfate process, either the usual or as modified, will generally contain a lower amount or proportion of sulfur, in comparison to the sodium, than the residual liquor from the sodium monosulfite process. When such sulfate process residual liquor is subjected to concentration and calcining or smelting, anelimination of sulfur occurs. Sulfur escaping with the furnace gases largely as sulfur dioxide or other compound may be recovered to a considerable extent where desired. The sodium content of the calcined product or smelt thus obtained will be mainly sodium carbonate, with small or moderate and varying amounts of other sodium salts, e. g., Na s, Na SO Some of the'sulfur may be converted into sodium sulfite and be present as such in the calcined product or melt.

The solution obtained from the calcined product or melt is then treated to form therefrom a cooking liquor for a sodium monosulfite process. Since this solution contains mainly sodium carbonate, it may in most cases, be subjected directly to sulfiting with sulfur dioxide to convert the sodium carbonate into sodium monosulfite. If the amount of sodium sulfid in the solution is such that a large amount of sodium thiosulfate might be formed by direct treatment with sulfur dioxide, the solution may be otherwise treated to convert the sodium carbonate into sodium sulfite. The solution which contains sodium carbonate may be subjected to sulfiting with sulfur dioxide either directly or indirectly to form the sodium monosulfite solution. \Vhen the solution contains mainly sodium carbonate and a substantial amount of sodium sulfide, the sodium carbonate may be converted to a large extent into sodium sulfite by treatment with a sufficient amount of calcium monosulfite, leaving sodium sulfide in solution along with the sodium sulfite. The sulfur for producing the sulfur dioxide or sodium bisulfite, or calcium monosulfite, used in sulfiting the sodium carbonate, may be obtained by the combustion of sulfur in a suitable sulfur burner.

In the cycle of operations above outlined it will be noted that the maximum sulfur content is present during the sodium monosulfite cook, that the sulfur content of the monosulfite residual liquor is converted in part by the residual liquor treatment into sodium sulfid, with elimination of some sulfur, and the production of a corresponding'amount of sodium carbonate; and that the sodium carbonate and sodium sulfid thus produced can advantageously be employed, e. g., after causticizing and adjusting where required. as the cooking liquor in the sulfate or modified sulfate process. It will further be seen that the residual liquor from the sulfate process, when subjected to the regenerating treatment, generally gives up considerable sulfur, and gives a product made up largely of sodium carbonate, such that it can advantageously be employed for the production of a suitable sodium monosulfite cooking liquor without the formation of any large amount of sodium thiosu'lfate.

lVhere the amount of sodium sulfid in the liquor produced by dissolving and causticizing the soda compounds obtained from the monosulfite residual liquor is proportionally higher, as compared to caustic soda, than that desired in the cooking liquor to be used in sulfate process, it is advantageous to return to the sulfate process, part of the residual liquor therefrom or the solution obtained by dissolving the compounds reclaimed from the residual liquor of that process, and which solution is made up largely of sodium carbonate. In other words, any desired amount of the sodium carbonate solution obtained from the sulfate process residual liquor, by the regenerating treatment, can be utilized for admixture with the sodium carbonate and sodium sulfid solution obtained from the monosulfite residual liquor, by regeneration, to give a regulated proportion of sodium carbonate and sodium sulfid for causticizing to produce the solution of caustic soda and sodium sulfid for a sulfate process. In such case, only the remaining amount of the sodium carbonate solution would be available for employment in making the sodium monosulfite cooking liquor for the monosulfite process, or some of the residual liquor from the sulfate process may be mixed with some of the residual liquor from the monosulfite process prior to the furnace treatment. In such cases. it may be advantageous to carry out two or more cooks using a sulfate process to one cook using a sodium monosulfite process.

During the regenerating treatment, some sodium sulfite may be formed and may be present in the solution of sodium carbonate and sodium sulfid, or of sodium carbonate, obtained from the calcined product or melt. This sodium sulfite may advantageously be present in a sulfate process cooking liquor, in which case the cooking liquor will contain sodium sulfite along with caustic soda and sodium sulfid. Also, some residual liquor from the monosulfite process may be used in the cooking liquor of the sulfate process. as it usually contains some sodium monosultite and thus modifies the reactions.

The invention will be further illustrated by the following specific examples and more detailed descriptions, but it will be understood that the invention is illustrated thereby and is not limited thereto.

The digesterused in the sodium monosulfite cooking process may be for example a vertical stationary digester of usual shape having, for example. a capacity of about 1,900 cu. ft. and provided with a perforated false bottom and a suitable steam ring placed just above the: perforated bottom, and provided with suitable cover, inlet and outlet alves, piping, etc.. so that the cooking may be carried out by the introduction of steam in suflicient amount and of suitable pressure and temperature at the lower end of the digester through the steam ring. The digester is provided with means for relieving gases therefrom occasionally or continuously dur ing the cooking operation and is provided with suitable blow-line for blowing the stock and residual liquor into a blow-pit when the cook has been finished. Saturated steam of about 160 to 165 lbs. gauge pressure per square inch is sufiicient for raising the temperature-within the digester to around 170 to 185 (3., and a gauge pressure. of around 135 to 140 lbs. per square inch in the upper portion of the digester.

The digester is charged with wood chips of the usual type, about 1; to along the grain, and the cooking liquor is a solution comprising primarily sodium sulfite as the active reagent. For a digester of the size mentioned, the cooking liquor may, for ex ample, equal about 1,000 to 1,300 cu. ft. which may be charged at a temperature of about 50 to 90 (1., and may contain about 6,500 to 8,000 lbs. of sodium sulfite (Na SO for about 7 to 8 cords of wood, when poplar, cottonwood, etc, are employed. The amount of sodium monosultite based on the bone-dry weight of the wood should be e. around 35 to 45%, or even more, using the larger amounts particularly for coniferous woods. The cooking liquor may also contain a small amount of caustic soda, sodium carbonate, sodium sulfid, sodium thiosulfate, or other sodium compounds, but sodium monosulfite is the preponderating active reagent.

lVith a charge of the character mentioned, a period of about 1 to 3 hours is used to bring the digester contents up to cooking temperature and pressure, with introduction of steam and producing a thorough circulation of the liquor within the digester and with occasional or continuous relief of vapors from the upper portion of the digester. The cooking treatment is continued until the stock has been cooked to the desired degree, which may be'from 3 to 10 hours. more or less, depending upon the particular wood to be cooked and the particular cooking liquor, temperature and pressure employed. When the cooking operation is completed, the stock is blown from the digester, together with the resid ual liquor. The residual liquor is separated from the pulp, and the pulp may be subjected to washing and further treatment in a manner which will be readily understood. e. the stock may be washed, then screened and thickened and bleached in the usual manner. if bleached pulp is desired.

The residual liquor separated from the pulp, together with wash waterfrom washing the pulp (which wash water may advantageously be kept as low as possible to avoid unnecessary dilution) may be in part used for diluting the strong solution of sodium sulfite charged into the digester. That is. this cooking liquor of the sodium monosulfite process may be made up in part of residual liquor from that process, or residual liquor diluted with wash water from the washing of the pulp. This may be advantageously done when the sodium sullite solution produced by the regenerating process, is stronger than needed ane requires dilution.

Some of the residual liquor from the sodium sulfite cooking process may likewise be used for diluting the solution of caustic soda and sodium sulfite for a. sulfate process, al though such cooking process may also be carried out without the use of any residual liquor as a part thereof.

For the most part, the residual liquor from the sodium ll'lOllOSLllfitG process, either alone or mixed with some residual liquor from the sulfate process, is subjected to a regeneration treatment by evaporation, e. g. in a multiple efi'ect evaporator until it reaches about 25 to 40 Baum, at about 150 F., and by further treating the concentrated residual liquor in a rotary calcining furnace, which mayor may not have a disc evaporator in'connection therewith, heated by the products of combustion of the organic matter and carbon, together with other fuel if desired or necessary. The product of the rotary furnace, either in a completely or partially carbonized form, may then if desired be fed into a smelting furnace of the usual soapstone type, operated so as to consume the organic matter and substantially all of the carbon, and produce a melt which consists primarily of sodium carbonate and sodium sulfid. This melt may contain, e. around 30 to 50%, more or less, of its sodium oxide content in the form of sodium sulfid, and the balance mostly as sodium carbonate. The melt is run into a suitable quantity of water or weak cooking liquor contained in a dissolver, with the addition of sufficient melt to produce a solution of about 2 to 25 Baum at about 150 F., more or less. The solution of sodium carbonate and sodium sulfid is then removed from the dissolver, for the most part, and more water or weak liquor added to the dissolver to prepare another batch of the solution by the addition of a suitable amount of the melt thereto. I

Instead of carrying out the calcining or smelting operation in a furnace of the smelting type, above described, the strong residual liquor may be treated in the rotary furnace such as is commonly used in soda process mills and subjected to a calcining and carbonizing treatment therein, with destruction of the organic matter to obtain a product which, e. g., on leaching, will give a solution similar to that obtained from the melt of the smelting furnace. In this case, however, it may contain a smaller amount of sodium sulfid in proportion to the sodium carbonate, and it may contain more sodium sulfite, sodium sulfate, etc., than is contained in the solution of the melt from the smelting furnace. For the most part, however, the solution of sodium compounds is made up primarily of sodium carbonate and sodium sulfid, particularly when the furnacing operation is carried out under strongly reducing conditions.

The strong, hot solution of sodium carbonate and sodium sulfid, obtained in the manner above described from the residual liquor of the sodium monosulfite process, is causticized with enough lime to produce a solution of caustic soda and sodium sulfid. After separating the solution from the lime mud, the lime mud is washed to regain more of the sodium compounds therefrom, and a sufficient amount of the washings added to the strong solution first taken off and mixed thoroughly therewith so as to obtain a solution of caustic soda and sodium sulfid of suffioient strength and suitable ratio to be used for the cooking liquor of a sulfate process. This cooking liquor will generally contain a moderate amount of sodium carbonate in addition to the caustic soda and sodium sulfid, owing to incomplete causticization. It may also have other sodium compounds in moderate and varying amounts, such as sodium sulfate, sodium sulfite, sodium thiosulfate, etc; but it is desirable to have a preponderating amount of the sodium present in the form of caustic soda and sodium sulfid, together with a moderate amount of sodium sulfite. Sodium carbonate should be kept low in amount in the cooking liquor. By regulating the causticizing operation, a suitable amount of the sodium carbonate can be converted into caustic soda. By using a moderate amount of calcium monosulfite along with calcium hydroxide, in the causticizing treatment, some of the sodium carbonate can be converted into sodium sulfite, especially where the amount of lime is kept sufiiciently below an amount which is chemically equivalent to the sodium carbonate.

The solution of caustic soda and sodium sulfid and without or with sodium sulfite thus obtained, with adjustment of strength and composition if needed, is then ready for use as cooking liquor of a sulfate process. About 900 to 1200 cu. ft. of cooking liquor is used for each digester of about 1,900 cu. ft. capacity described above. Some of the residual liquor from a sulfate process, or some of the residual liquor from a sodium monosulfite process, may be added to the cooking liquor, particularly where the dilution of it is desired. The wood cooked may be either deciduous or coniferous. Generally, the amount of total caustic soda and sodium sulfid will be around 16% to 25% on the bonedry weight of the wood. In general, if the best yields and the best quality of pulp are to be obtained, including pulp of good strength, the amount of active chemical should be kept fairly low, but nevertheless using sufficient active chemical to produce a satisfactory cook. The cooking liquor may advantageously contain a higher percentage of its total active chemical in the form of sodium sulfid than in the usual sulfate process cooking liquor. In such a case, the liquor is a milder cooking liquor than one in which the sodium sulfid is low and the caustic soda is very high. The ratio of caustic soda to sodium sulfid can, however, be regulated and controlled, e. g., as hereinbefore mentioned, and as elsewhere more fully described.

Another advantage obtained when the amount of total caustic soda and sodium sulfid is kept low, is that when the residual liquor from this sulfate cook is evaporated and the organic matter consumed in the rotary furnace under mild reducing conditions or even under oxidizing conditions, the sodium compounds thus regained will contain primarily sodium carbonate, and in fact, may have very little, if any, sodium sulfid therein, most of the sulfur under such conditions either going off with the products of combustion or remaining in the recovered sodium compounds, e. g., as sodium sullite and sodium sulfate.

The solution of sodium carbonate thus recovered, and which may contain varying amounts of other soduim salts, may be treated with sulfur dioxide gas or with sodium bisulfite or with an alkaline earth metal sulfite to convert sodium carbonate into sodium sulfite. The sodium sulfite solution thus obtained can then be used as the cooking liquor in a sodium monosullite cooking process with proper regulation of the strength (and com position if needed) of the solution and with the addition, if desired, of some of the residual liquor from the sodium monosulfite process. Additions of Na COS, NaOH, Na SO or Na SO may be made to replace the soda lost in operations, at any suitable point or points.

Instead of using all of the sodium carbonate solution. regenerated from sulfate residual liquor, for the production of sodium monosulfite cooking liquor, a part of the liquor may be added to the solution of sodium carbonate and sodium sulfid, which is to be used in making the cooking liquor for sulfate process. In this way, the sodium carbonate content of such a liquor can be increased and the sodium sulfid proportion correspondingly reduced. When the mixed solutions are then subjected to the causticizing operation. a correspondingly increased amount of caustic soda may be produced. By regulating the amount of sodium carbonate solution (obtained from a sulfate process residual liquor treatment) to be mixed with the solution of sodium carbonate and sodium sulfid from a 'monosulfite residual liquor treatment, the ratio of sodium carbonate to sodium sulfid can be regulated and controlled, and the proportion of caustic soda to sodium sulfid can correspondingly be regulated and controlled; thus enabling uniformity of cooking liquors to be obtained.

lVhere any considerable amount of sodium carbonate obtained by a sulfate residual liquor treatment is employed in making further amounts of cooking liquor for a sulfate process, in the manner above described, the amount of sodium carbonate available for sulfiting either directly or indirectly to form sodium monosulfite for a sodium monosulfite process, will be correspondingly reduced. For this reason, as above mentioned, it may be advantageous to carry out a greater number of cooks, or to operate a larger number of digesters, with a sulfate process, than with a sodium monosulfite process, thus balancing the operations of the entire plant, or of such digesters ofthe plant as are operated upon a monosulfite process and a sulfate process respectively.

These processes may be employed upon woods of the same or of different kinds. In general, coniferous woods, such as spruce, and especially the highly resinous pines, like jack-pine and shortleaf pine, require more of the active chemicals per ton of pulp for their satisfactory cooking, than deciduous Woods, such as cotton-Wood, poplar, birch, beech, maple, alder, etc.

The loss of sodium compounds in the processes may be made up, for example, by adding sodium carbonate either to the solution of sodium carbonate and sodium sulfid before causticizing, or advantageously to the sodium carbonate solution which is to be sulfited for the production of sodium monosulfite. it may also be made up by adding caustic soda e. g. to the cooking liquor of a sulfate process. Sodium sulfate may also be used for making up all or part of the soda losses and added e. to the residual liquor or to the calcined product charged into the furnace, the sodium sulfate being reduced and increasing the amount of sodium sulfid that is formed. Sodium sulfite may be prepared from sodium chloride and added to either type of cooking liquor.

It will thus be seen that the present invention provides a cyclic series of operations in which sodium monosulfite and sulfate processes are advantageously combined in the cycle, and that the sodiumsulfite used in a sodium sulfite process supplies part or all of the sodium and sulfur used in a sulfate process, by treatment of the residual liquors from a monosulfite process in the manner above described. It will also be seen that the residual liquor from a sulfate process is treated so that a preponderating amount of the sodium content thereof is made available for the production of sodium sullite for use in a monosulfite process. The two cooking liquors, i. e. the sodium monosulfite cooking liquor, and the caustic soda and sodium sulfid cooking liquor, are respectively regenerated in whole or in part from the resid ual liquor of the process in which the other cooking liquor was employed. The same sodium thus goes through the entire cycle of operations, e. g. being used first as sodium sulfite, being then converted into a mixture of caustic soda and sodium sulfid, and again into sodium sulfite. The sulfur of the sodium sulfite is in part driven off during the first regenerating treatment, and the remainder is, for a considerable part, driven off during the second regenerating treatment; and the sulfur thus driven off, partly as sulfur dioxide, can be recovered in part by scrubbing the stack gases, and made available again for converting sodium carbonate into sodium sulfite, etc. for further use in the process. Generally the stack gases thus treated do not contain sufiicient sulfur dioxide, and a further amount of-sulfur dioxide should be formed from sulfur in suitable sulfur burners. The raw materials for the process are thus made up of sulfur to supply the loss of sulfur, of lime for the causticizing operation, and of sodium carbonate, sodium sulfate or other sodium compound to supply the sodium lost during the process.

The combination of the new processes in the manner described, presents the advantage among others, that the sulfur of the sodium sulfite, which is primarily or entirely relied upon in one process, is employed, after it has served its purpose in that process, for the production of a cooking liquor comprising a large amount of sodium sullid, with the sodium sulfid directly produced in a usable form from the sodium sulfite residual liquor. Only a causticizing treatment is required to convert sodium carbonate into caustic soda when a solution of caustic soda and sodium sulfid is desired for a sulfate process. The residualliquor from such a sulfate process, when subjected to the regenerating treatment, gives up sufficient of its sulfur so that the amount retained is not excessive when the product is sulfited for the production of the sodium monosulfite cooking liquor especially where there is little if any N s along with the Na CO Considerable Na SO may be present e. g. due to oxidation treatment, as it returns to the sulfate type liquor when reduced to N 21 8. here the sullid content of the smelt or calcined product produced from a sulfate residual liquor is low, it is not necessary to employ special methods of sulfiting to avoid the production of objectionable amounts of thiosulfate, although some sodium thiosulfate may be present in the cooking liquor of a sodium monosulfite process. When present, it will also serve to furnish an additional source of sulfur for the production of sodium sulfid during the subsequent treatment of the residual liquor from a sodium sulfite process and thus serves a useful purpose in the cycle. Na SO also produces some Na S when reduced.

In referring to the 'sulfate'process, we do not limit ourselves to the sulfate process as commonly practiced or commonly understood,-but use this term to include processes in which the activity of the cooking liquor is made up largely or for the most part or entirely of caustic soda and sodium sulfid,

whether the proportions of caustic soda and sodium sulfid be the same or different from those of the usual cooking liquors of the ordinary sulfate process, and even though other sodium salts, especially sodium sulfite may be present therewith in the cooking liquor. In some cases the Na s, Na CO3 liquor may be used for cooking without bein treated with Ca(OH) 1 Tn referring to the sodium monosuliite process we include those cooking liquors which are made up entirely of a solution of sodium monosulfite, and also those cooking liquors which comprise a preponderating amount of sodium monosulfite together with small amounts of any of the following compounds, viz; sodium sulfide, sodium hydroxide, sodium thiosulfate, sodium carbonate, sodium sulfate.

We claim:

1. The method of producing wood pulp from wood which comprises cooking wood in a non-acid sodium monosulfite cooking liquor, cooking wood in an alkaline cooking liquor comprising sodium sulfid, and recovering sodium compounds from the residual liquor resulting from each digestion and using the same in the formation of the cooking liquor for the other digestion.

2. The method of producing wood pulp from'wood which comprises cooking wood in a non-acid sodium monosulfite cooking liquor, subjecting the residual liquor from such cooking operation to a carbonizing and reducing treatment, with resulting production of sodium carbonate and sodium sulfid, and treating the resulting product for the production of a cooking liquor comprising caustic soda and sodium sulfid, said treatment including a causticizing treatment to convert sodium carbonate into caustic soda.

3. The method of producing wood pulp from wood which comprises cooking wood with an alkaline cooking liquor comprising sodium sulfid, treating the residual liquor from the process by a concentrating and carbonizing treatment to give a product containing the sodium salts mainly as sodium carbonate, and treating this product to produce sodium monosulfite therefrom, said treatment including a sulfiting treatment to convert sodium carbonate into a non-acid solution of sodium monosulfite, and cooking wood with the sodium monosulfite containing solution so produced. r

4. The method of producing wood pulp from wood which comprises cooking wood in a non-acid sodium monosulfite cooking liquor, cooking wood in a cooking liquor comprising sodium sulfid, treating the residual liquor from the monosulfite cooking process for the production of cooking liquor for the other-process, and treating the residual liquor, from the process in which sodium sulfid is used, to produce from a part of the soda compounds thereof a cooking liquor for a monosulfite cooking process.

5. The method of producing Wood pulp from wood which comprises cooking Wood in a cooking liquor containing sodium sulfid as one of its primary cooking reagents, treating the residual liquor from such process by a concentrating and calcining treatment, the treatment including an oxidizing treatment to give a product containing the sodium salts mainly as sodium carbonate and sodium sulfate, forming a solution of such salts and sulfiting the same to produce a non-acid sodium monosulfite cooking liquor, cooking wood with the liquor so produced, and treating the residual liquor from such sulfite cooking process by subjecting it to concentration and a reduction treatment to give a product containing sulfide, forming a solution of the resulting product and treating the same to produce a sulfide-containing cooking liquor.

6. The method of treating cellulosic fibre bearing material, which comprises a digesting treatment of fibrous material of wood origin in a non-acid cooking liquor containing sodium monosulfite, a digesting treatment of fibrous material of wood origin in an alkaline cooking liquor containing an alkaline compound of sodium, recovering sodium com pounds from residual liquor resulting from each digestion, treating the same to'form a cooking liquor, and using such cooking liquor in the other of the said digesting treatments.

7. The further improvement in the process of claim 6, characterized by the use of sodium sulfid in the said alkaline cooking liquor.

8. The method of treating cellulosic fibre bearing material, which comprises a digest ing treatment of fibrous material of wood origin in a non-acid cooking liquor containing sodium monosulfite, a digesting treatment of fibrous material of wood origin in an alkaline cooking liquor containing an alkaline sodium compound, recovering an alkaline compound of sodium from residual liquor from the firstmentioned digesting treatment, treating the same to form an alkaline cooking liquor, and using this cooking liquor in the second-mentioned digesting treatment.

9. The method of treating cellulosic fibre bearing material, which comprises a digesting treatment of fibrous material of Wood origin in a non-acid cooking liquor containing sodium monosulfite, a digesting treatment of fibrous material of wood origin in an alkaline cooking liquor containing an alkaline sodium compound, recovering an alkaline compound of sodium from residual liquor from the second-mentioned digesting treatment, treating the same to "form a cooking liquor containing sodium monosulfite, and using this cooking liquor in the first-mentioned digesting treatment.

10. The method of producing wood pulp from wood, which comprises digesting wood in a non-acid cooking liquor containing sodium monosulfite, digesting wood in an alkaline cooking liquor containing sodium sullid and sodium hydroxide, and recovering sodium compounds from the residual liquor resulting from each digestion and using the same in the formation of the cooking liquor for the other digestion.

11. In a method of producing pulp by digestion with chemical agents the cyclic process, which comprises subjecting residual non fibrous material, resulting from digesting cellulosic fibre bearing material With a non-acid cooking liquor including a dissolved monosulfite, to a furnacing treatment adapted to form an ash containing a carbonate and a sulfur-containing compound derived at least in part from said sulfite, treating this product to produce a chemical digesting liquor including a hydroxide and a sulfid, digesting cellulosic fibre bearing material with the liquor thus formed, subjecting residual nonfibrous material resulting from this digesting step to a furnacing adapted to form an ash containing a carbonate and a substantially smaller amount of sulfur-containing compounds derived at least in part from the hydroxide and sulfid, treating the ash to form a non-acid chemical digesting liquor including a monosulfite so that a substantial portion of the monosulfite is derived from sulfur-containing compounds of the 'last named ash without passing through an additional furnacing treatment.

12. In a method of producing pulp, the cyclic process which comprises subjecting residual non-fibrous material, resulting from digesting cellulosic fibre bearing material with a non-acid digesting liquor including sodium monosulfite, to a furnacing treatment adapted to form a furnace product containing sodium carbonate and a sulfurcontaining sodium compound derived at least in part from said sulfite, treating this product to produce an alkaline digesting liquor containing sodium hydroxide and sodium sulfid as its main digesting reagents, digesting cellulosic fibre bearing material with the liquor thus formed, subjecting residual nonfibrous material, resulting from this digesting step, to a treatment including a sulfiting operation adapted to form a non-acid digesting liquor including a sulfite of sodium as a primary digesting reagent, and treating cellulosic fibre bearing material therewith according to the first-mentioned digesting op eration.

13. The process which comprises the following steps: subjecting cellulosic-fibrebearing material to a solubilizing treatment by means of liquor including a sulfur-free alkaline compound of an alkali metal; subjecting alkali metal bearing matter derived at least in part from the said compound and including sulfur-bearing matter, to a furago nacing treatment, thereby forming a furnaceproduct including a substantial amount of alkali metal carbonate and a lesser but substantial amount of a sulfur-bearing compound of an alkali metal; treating at least a portion of such alkali-metal carbonate and sulfur-bearing compound of an alkali metal so as to form monosulfite of an alkali metal in larger amount than alkali metal thiosulfate and so that at least a portion of such sultite is derived from such alkali metal sulfur-bearing compound without most of the alkali metal content of such treated portion being utilized as alkali metal hydroxide and alkali metal sulfid for an intervening digesting' treatment of wood so as to produce chemical pulp, and using monosulfite of an alkalimetal thus formed in a treatment for solubilizing organic material contained in cellulosic-fibre-bearing material.

14. The method of producing wood pulp from wood, which comprises cooking wood in a non-acid sodium monosulfite cooking liquor, cooking wood in an alkaline cooking liquor comprising sodium hydroxide and sodium sul fid as its principal digesting reagents, mixing the residual liquors from these cooking operations, removing water therefrom, furnacing the residue to form a furnace product containing sodium carbonate and sodium sulfid, treating the furnace product so asto pro duce a cooking liquor suitable for use in either of the said cooking operations, and cooking wood therewith.

In testimony whereof we afiix our signatures.

LINN BRADLEY. EDWARD P. MGKEEFE. 

